PROJECT SUMMARY More than 6.5 million American adults have HF, which results in approximately 1 million hospital admissions per year in patients 65 year and older. Hospitalized patients with HF have a 30-day mortality rate of approximately 10%. Cardiac rehabilitation (CR), a multidisciplinary structured secondary prevention program that applies effective lifestyle therapies (diet, exercise, stress reduction, smoking cessation, weight loss, etc.) to reduce the risk of secondary cardiac events and improve functional status, has demonstrated a modest reduction in all-cause mortality in patients with HF and reduced ejection fraction (HFrEF). Randomized controlled studies of patients with HFrEF or HF with preserved ejection fraction have reported that CR improves symptoms, increases aerobic capacity, endurance, improves self-reported quality of life, and reduces rehospitalization. The American Heart Association and the American College of Cardiology recommend exercise training for patients with HF, and, in 2014, the Centers for Medicare and Medicaid Services began to cover CR for patients with HFrEF. However, national data suggest that only 2-10% of patients with HF attend CR after a hospitalization and our preliminary data suggest that little improvement has occurred since 2014. Our long-term goal is to identify effective delivery-system interventions that improve the health and outcomes of patients with HF. The objective of this proposal is to identify implementation strategies that increase participation in CR among patients with HF. Then with a group of clinicians, patient advocacy organizations, CR leaders, policymakers, and payers, we will prioritize strategies that are the most acceptable, feasible, and responsive to the needs of the community. In Aim 1, we will analyze Medicare claims among recently hospitalized HF patients to identify hospital-referral regions (HRRs) that are most and least successful in recruiting recently hospitalized patients with HF to CR. Beginning with these programs, we will use the Consolidated Framework for Implementation Research (CFIR) to guide qualitative interviews of clinicians with these HRRs, identifying facilitators and barriers to CR participation. We will present our findings to a panel of stakeholders who will prioritize strategies. We will then pilot these strategies in a subset of CR practices in order to refine the final set of recommendations that will inform practice (e.g., outpatient and inpatient clinicians, CR programs, patients), policy (e.g., clinical practice guidelines and reimbursement strategies), and future research (e.g., implementation trials). These activities are highly responsive to the STIMULATE RFA because they are timely, engage a range of stakeholders, and examine implementation of an underutilized evidence-based intervention. They are also consistent with National Heart, Lung, and Blood Institute's Strategic Goals and Objectives, specifically objective 6, which aims to ?optimize translational, clinical, and implementation research to improve health and reduce disease.?